1. Field of the Invention
The present invention relates to a novel liquid crystal polyester which is melt-moldable, having high strength and high modulus of elasticity, and which is less anisotropic in mechanical properties when molded, exhibiting under a certain condition selective reflection in the visible light region.
2. Description of the Related Art
Recently, demand of materials superior in rigidity, heat-resistance, and chemical resistance has been increasing in all of the fields of fibers, films, and molded articles. Most of polyesters, which are used widely for general molded articles, are inferior in mechanical properties such as flexural modulus, etc., and are not suitable for the uses where high strength and high modulus of elasticity are required. Although blending of a filler or a reinforcing agent such as calcium carbonate, glass fiber, and the like is known to be effective in improving such mechanical properties, the blended materials involve various practical problems such that the specific gravity of the blended materials tend to increase to cancel the lightweight property, and abrasion of a molding machine during molding is serious
Liquid crystal polyesters have recently attracted attention as a polyester which does not require the addition of a reinforcing agent and is suitable for uses requiring high strength and high modulus of elasticity. Particular attention has been given to the liquid crystal polyesters, since a thermoplastic liquid crystal polyester consitituted from polyethylene terephthalate and hydroxybenzoic acid was disclosed by W. J. Jackson in U.S. Pat. No. 3,804,805, and in J. Polymer Science polymer Chemistry Edition, Vol. 14, p.2043, (1976). Since then, various liquid crystal polyesters have been studied to develop polyesters having simultaneously high strength, improved rigidity, and melt-moldability. However, few molded articles have been found which is free from the above problems. This is because those liquid crystal polymers exhibit high orientation in a molten state, giving great anisotropy in the mechanical properties thereof.
For cancelling the anisotropy, a method was disclosed which employs cholesteric liquid crystal polymer by W. R. Krigbaum (U.S. Pat. No. 4,412,059). This method, however, is disadvantageous in that the rate of transesterification is low, and optically active units cannot be introduced in an arbitrary amount into the polymer, and further that the physical properties become impaired, or the liquid crystal-forming region is lowered depending on the bonding type of the structural units.